Arthur J. Gallagher & Co. (AJG)

Founded in 1927 as a one-person agency, Gallagher's primary business is insurance brokerage, with a focus on serving middle-market companies. The company's risk management segment provides third-party claims adjustment to companies that choose to self-insure. Gallagher has about 72,000 employees and generates about a third of its revenue internationally, primarily in Australia, Canada, New Zealand, and the UK.